With reference to photocopying machines of the diazo type, it has been customary in one form of machine to develop the copy paper by feeding it past a mouth of a development chamber which applies a gaseous developing agent such as ammonia to the surface of the sheet. In this circumstance, the sheet must be fed reliably past the mouth of the chamber in fairly close contact with the mouth margins.
Various types of feeding systems have been developed for this purpose, but one type which has proven to be rather effective, while also being mechanically simple and relatively inexpensive to produce, involves the use of an elongate drum or transport roll which mates with the development chamber mouth and frictionally feeds the paper past the mouth at the appropriate development speed.
In devices of the kind just described, reliance for proper feeding action is placed entirely upon the frictional contact between the roll and the paper surface, and to assure this contact there is provided a sheet of antifriction material such as "Teflon" spanning the mouth of the development chamber and snugly embracing the adjacent portion of the roll. The copy paper is fed between the roll and the antifriction sheet which presses the copy sheet against the frictional surface of the roll. The antifriction sheet also has many perforations to permit access of the developing gas to the light sensitive surface of the paper.
The roll is conventionally formed from a long tube of metal such as aluminum. The term "aluminum" when used herein will be understood to include not only pure aluminum but also anodizable aluminum alloys in which the principle metal is aluminum. The frictional properties of the roll are enhanced by mechanical roughening procedures such as sand blasting, and treatment is provided to prevent wear of the roughened surface by contact with the paper. One customary treatment is to anodize the surface of the roll. So far as can be determined it has been customary to provide on the surface of the roll, a degree of roughness having an RMS value of about 100 microinches.
Apparatus of the above description is used with reasonable success, but has a certain operational drawback which it would be desirable to avoid if possible. This drawback is of such character that, if it were possible to eliminate its effect, acceptance of this type of equipment would be markedly improved.
Reference is had particularly to operator responsibility in connection with maintenance of the machine. For some reason the frictional properties of the roll are found to be rather variable depending upon the amount of use. This may be due to the fact that material from the antifriction sheet surface, or from the copy paper, gradually accumulates and tends to fill the depressions in the roughened roll surface so that the roll surface becomes smoother, in effect, and fails to feed the copy paper reliably. Whatever the cause, the prior art has determined that cleaning of the surface will substantially restore the frictional properties, and the customary instructions in the operator's manual provide for cleaning the roll surface once a week to avoid undue deterioration of its frictional properties.